Long Slit Spectra at Low Resolution (R<1800)

1800 either with short cameras and 0.3 arcsec wide slit or with long cameras and 0.1 arcsec wide slit. Lower resolving powers if wider slits are used.

Typical uses:(...and limitations)

Spectrum of all or
most of an atmospheric window or filter passband as defined by the blocking filter (X, J, H, K, L, or M) at one
grating setting with 99 arcsec long slit

The minimum usable wavelength for long slit spectroscopy is ~1.03um observed in 6th order. Use the cross-dispersing prism for wavelengths shorter than 1.03 microns. In addition, the wavelength ranges 1.37-1.47, 1.82-1.91, and 2.49-2.56 microns are not covered by the blocking filters; they can only be observed in cross-dispersed mode.

When viewing an X band spectrum, signal at apparent wavelengths shorter than 1.00 um is from 5th order at the long wavelength end of the X filter; likewise signal at wavelengths greater than 1.18 microns is the 7th order spectrum at the short wavelength end of the X filter.

Likewise, in the J band (5th order) signal at apparent wavelengths below 1.15 microns is actually 4th order light near 1.4 microns; likewise the spectrum apparently beyond 1.40 microns is 6th order light near 1.2 microns.

In the H band (order 4) the spectrum beyond an apparent wavelength of 1.85 microns is the 5th order spectrum at the short wavelength end of the H filter.

Note also that the spectral coverage in the L window is "only" 0.99 microns, and thus the full window cannot be covered in one grating setting. For example, two setting would be required to cover both the water ice band near 3.0 microns and the Br alpha line at 4.05 microns.

Large observing overheads mean that the 32 l/mm grating and short red camera should generally not be used for M band spectroscopy. Use the 111 l/mm grating instead.